It is known in the art to use carbon films as electron sources in field emission devices. Electron-emissive films can provide higher emission density (electron current per unit area) than prior art Spindt tips. However, prior art carbon films suffer from several disadvantages. For example, the uniformity of the emission current across the film is typically poor and not reproducible.
It is known in the art to produce field emitted electrons from films having nanotubes. For example, Heer, et al. describe a method for forming a film of nanotubes oriented perpendicular to the plane of the film ("A Carbon Nanotube Field-Emission Electron Source", Science, Volume 270, Nov. 17, 1995, pp. 1179-1180.) The method of Heer, et al. includes first producing a macroscopic bundle of carbon, which is then purified. This prior art method further includes a step for separating the nanotubes to achieve a narrow size distribution. The narrow size distribution is preferred because the electrical properties of the nanotubes are highly dependent on their length and diameter. Then, a step is included for orienting the nanotubes perpendicularly with respect to the surface of the film. The film described by Heer, et al. further includes a polytetrafluoro-ethylene substrate, in which the nanotubes are anchored.
Accordingly, there exists a need for an improved electron-emissive film, which exhibits uniform electron emission, has low electric field requirements, and has simpler fabrication requirements than those of prior art electron-emissive films.